Graded throttling for network-on-chip traffic

ABSTRACT

Graded throttling for network-on-chip traffic, including: calculating, by an agent of a network-on-chip, a number of outstanding transactions issued by the agent; determining that the number of outstanding transactions meets a threshold; and implementing, by the agent, in response to the number of outstanding transactions meeting the threshold, a traffic throttling policy.

BACKGROUND

Chips such as systems-on-a-chip use a network-on-chip to facilitatecommunication between functional components. As traffic on thenetwork-on-chip increases, the risk of degraded performance alsoincreases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a chip for graded throttling fornetwork-on-chip traffic according to some embodiments.

FIG. 1B is a block diagram of a chip for dynamic network-on-chip trafficthrottling according to some embodiments.

FIG. 2 is a flowchart of an example method for graded throttling fornetwork-on-chip traffic according to some embodiments.

FIG. 3 is a flowchart of an example method for graded throttling fornetwork-on-chip traffic according to some embodiments.

FIG. 4 is a flowchart of an example method for graded throttling fornetwork-on-chip traffic according to some embodiments.

FIG. 5 is a flowchart of an example method for graded throttling fornetwork-on-chip traffic according to some embodiments.

FIG. 6 is a flowchart of an example method for dynamic network-on-chiptraffic throttling according to some embodiments.

FIG. 7 is a flowchart of an example method for dynamic network-on-chiptraffic throttling according to some embodiments.

FIG. 8 is a flowchart of an example method for dynamic network-on-chiptraffic throttling according to some embodiments.

FIG. 9 is a flowchart of an example method for dynamic network-on-chiptraffic throttling according to some embodiments.

DETAILED DESCRIPTION

In some embodiments, a method of graded throttling for network-on-chiptraffic includes, among other elements calculating, by an agent of anetwork-on-chip, a number of outstanding transactions issued by theagent. Such graded throttling also includes determining that the numberof outstanding transactions meets a threshold. In response todetermining that the number of outstanding transactions meets thethreshold, the graded throttling may be carried out by implementing, bythe agent, a traffic throttling policy.

In some embodiments, the number of outstanding transactions includes adifference between a number of issued transactions that have notreceived a response by the agent. In some embodiments, the threshold isincluded in a plurality of thresholds and the traffic throttling policyis included in a plurality of throttling policies. In such embodiments,implementing the transaction policy includes implementing thetransaction policy based on which of the plurality of thresholds is metby the number of outstanding transactions. In some embodiments, thegraded throttling for network-on-chip traffic includes recalculating thenumber of outstanding transactions issued by the agent and determiningthat the number of outstanding transactions falls below the threshold.Responsive to such a determination, the agent ends the trafficthrottling policy. In some embodiments, ending the transaction policyincludes implementing another throttling policy. In other embodiments,ending the transaction policy includes issuing transactions withoutthrottling. In some embodiments, determining that the number ofoutstanding transactions falls below the threshold includes determiningthat the number of outstanding transactions falls below the threshold bya predefined amount.

In some embodiments, a chip for graded throttling for network-on-chiptraffic performs steps including calculating, by an agent of anetwork-on-chip, a number of outstanding transactions issued by theagent. Such graded throttling also includes determining that the numberof outstanding transactions meets a threshold. In response todetermining that the number of outstanding transactions meets thethreshold, the graded throttling may be carried out by implementing, bythe agent, a traffic throttling policy.

In some embodiments, the number of outstanding transactions includes adifference between a number of issued transactions that have notreceived a response by the agent. In some embodiments, the threshold isincluded in a plurality of threshold and traffic throttling policy isincluded in a plurality of throttling policies. In such embodiments,implementing the transaction policy includes implementing thetransaction policy based on which of the plurality of thresholds is metby the number of outstanding transactions. In some embodiments, thesteps include recalculating the number of outstanding transactionsissued by the agent and determining that the number of outstandingtransactions falls below the threshold Responsive to such adetermination, the agent ends the traffic throttling policy. In someembodiments, ending the transaction policy includes implementing anotherthrottling policy. In other some embodiments, ending the transactionpolicy includes issuing transactions without throttling. In someembodiments, determining that the number of outstanding transactionsfalls below the threshold includes determining that the number ofoutstanding transactions falls below the threshold by a predefinedamount.

In some embodiments, an apparatus for graded throttling fornetwork-on-chip traffic includes a chip that performs steps includingcalculating, by an agent of a network-on-chip, a number of outstandingtransactions issued by the agent. Such graded throttling also includesdetermining that the number of outstanding transactions meets athreshold. In response to determining that the number of outstandingtransactions meets the threshold, the graded throttling may be carriedout by implementing, by the agent, a traffic throttling policy.

In some embodiments, the number of outstanding transactions includes adifference between a number of issued transactions that have notreceived a response by the agent. In some embodiments, the threshold isincluded in a plurality of threshold and traffic throttling policy isincluded in a plurality of throttling policies. In such embodiments,implementing the transaction policy includes implementing thetransaction policy based on which of the plurality of thresholds is metby the number of outstanding transactions. In some embodiments, thesteps include recalculating the number of outstanding transactionsissued by the agent and determining that the number of outstandingtransactions falls below the threshold Responsive to such adetermination, the agent ends the traffic throttling policy. In someembodiments, ending the transaction policy includes implementing anotherthrottling policy. In other some embodiments, ending the transactionpolicy includes issuing transactions without throttling. In someembodiments, determining that the number of outstanding transactionsfalls below the threshold includes determining that the number ofoutstanding transactions falls below the threshold by a predefinedamount.

FIG. 1A is a block diagram of a non-limiting example chip 102 a. Theexample chip 102 a can include a variety of chips, includingmicroprocessors, integrated circuits, or systems-on-a-chip. The examplechip 102 a can be implemented in a variety of computing devices,including mobile devices, personal computers, peripheral hardwarecomponents, gaming devices, set-top boxes, and the like. The chip 102 aincludes a plurality of agents 104 a-n. The agents 104 a-n arefunctional units or hardware modules of the chip 102 a. For example, insome embodiments, the agents 104 a-n include various modules of asystem-on-chip architecture.

To facilitate communication between agents 104 a-n, the chip 102 a alsoincludes a plurality of routing agents 106. The routing agents 106include hardware modules that switch and/or route traffic and/ormessages between agents 104 a-n. Accordingly, the routing agents 106implement a network-on-chip 108. In some embodiments, thenetwork-on-chip 108 includes a packet switching network of routingagents 106.

Communication between the agents 104 a-n is decentralized in that noagent 104 a-n has direct knowledge of the state (e.g., trafficgeneration, responses, queues, etc.) of other agents 104 a-n and therouting agents 106, and there is no centralized entity managing thetraffic generation and/or response behaviors of the agents 104 a-n.Thus, the agents 104 a-n have no direct knowledge of whether thenetwork-on-chip 108 is being overloaded or approaching capacity forrouting traffic and have no direct knowledge of whether or not tothrottle traffic generation accordingly.

To improve performance of traffic via the network-on-chip 108, eachagent 104 a-n uses a number of outstanding transactions issued by thatagent 104 a-n as an estimate of the state of the network-on-chip 108. Anumber of outstanding transactions for a given agent 104 a-n is a numberof messages sent via the network-on-chip 108 to other agents 104 a-nexpecting a response (e.g., a response to a request, an acknowledgementof receipt) that has not been received. As communication via thenetwork-on-chip 108 slows or the routing agents 106 are handlingincreased amount of traffic, the time for an agent 104 a-n to respond toa message will increase. Accordingly, the number of outstandingtransactions for a given agent 104 a-n will increase assuming the rateof transaction generation for that agent 104 a-n does not decrease.

In order to implement grading throttling for network-on-chip 108traffic, an agent 104 a-n will calculate a number of outstandingtransactions issued by the agent 104 a-n. The agent 104 a-n will thencompare the number to a threshold. Where the number falls below thethreshold, the agent 104 a-n will continue to generate traffic accordingto a currently implemented traffic throttling policy, if any. A trafficthrottling policy is a configurable or programable limit at which agiven agent 104 a-n generates traffic for the network-on-chip 108. Wherethe number exceeds the threshold, the agent 104 a-n will implement atraffic throttling policy. For example, assume that an agent 104 a-n isgenerating traffic for the network-on-chip 108 independent of anytraffic throttling policy (e.g., without a limit). In response to thenumber of outstanding transactions for that agent 104 a-n meeting athreshold, the agent 104 a-n will then implement a traffic throttlingpolicy to impose a limit on a rate at which the agent 104 a-n providestraffic to the network-on-chip 108.

In some embodiments, the threshold is one of a plurality of thresholdsand the traffic throttling policy is one of a plurality of trafficthrottling policies. For example, in some embodiments, each trafficthrottling policy corresponds to one of the plurality of thresholds suchthat, when the number of outstanding transactions for a given agent 104a-n exceeds a given threshold, the corresponding traffic throttlingpolicy is implemented. For example, a first threshold corresponds to afirst traffic throttling policy (e.g., a “light throttling policy”), asecond threshold higher than the first threshold corresponds to a secondtraffic throttling policy more restrictive than the first trafficthrottling policy (e.g., “a heavy throttling policy”), and a thirdthreshold greater than the second threshold corresponds to a thirdtraffic throttling policy where the agent 104 a-n ceases to generatetraffic (e.g., a “stop throttling policy”).

Using this example, where the number of outstanding transactions for anagent 104 a-n crosses the first threshold, the agent 104 a-n willimplement the light throttling policy. If the number of outstandingtransactions for the agent 104 a-n continues to increase even though thelight throttling policy is implemented, and the number crosses thesecond threshold, the agent 104 a-n will implement the heavy throttlingpolicy. Should the number continue to increase and meet the thirdthreshold, the stop throttling policy will be implemented.

The agent 104 a-n will continually (e.g., at a predefined interval)recalculate the number of outstanding transactions for that agent. Wherethe number of outstanding transactions falls below the threshold (e.g.,the last satisfied or crossed threshold), the agent 104 a-n ends thecurrently implemented traffic throttling policy. In some embodiments,this includes removing any implemented traffic throttling policy andissuing traffic to the network-on-chip 108 without restriction. In otherembodiments, this includes implementing another (e.g., a lessrestrictive) traffic throttling policy. Continuing with the exampleabove, assuming an agent 104 a-n is implementing a heavy throttlingpolicy, where the number of outstanding transactions falls below thesecond threshold and is still above the first threshold, the agent 104a-n will implement the light throttling policy instead of the heavythrottling policy.

Were an agent 104 a-n to end an implemented throttling policy when thenumber of outstanding transactions falls below the threshold, the numberof outstanding transactions runs a risk of quickly increasing, therebycrossing the threshold again and causing the traffic throttling policyto be reimplemented. This would result in the agent 104 a-n oscillatingbetween implementing and ending a traffic throttling policy as thenumber of outstanding transactions oscillates between meeting andfalling below the threshold. To prevent this, in some embodiments, anagent 104 a-n ends an implemented throttling policy in response to thenumber of outstanding transactions falling below the correspondingthreshold by a predefined amount. Continuing with the example above,assume that the first threshold is fifty outstanding transactions.Further assume that the number of outstanding transactions has exceededthe first threshold and that the light throttling policy is in place.Instead of removing the light throttling policy when the number ofoutstanding transactions falls below fifty, the agent 104 a-n removesthe light throttling policy when the number of outstanding transactionsfalls ten transactions below the threshold (e.g., forty outstandingtransactions).

FIG. 1B is a block diagram of a non-limiting example chip 102 b. Theexample chip 102 b is similar to the chip 102 a of FIG. 1A in that theexample chip 102 b includes a plurality of agents 104 a-ncommunicatively coupled via a network-on-chip 108 of a plurality ofrouting agents 106. In some embodiments, the agents 104 a performsimilar graded traffic throttling as was described with respect to FIG.1A. The chip 102 b differs from the chip 102 a in that the chip 102 bincludes a plurality of detector modules 110. Detector modules 110 arehardware components included in or coupled to agents 104 a-n and/orrouting agents 106. Although FIG. 1B shows each agent 104 a-n and therouting agents 106 as having corresponding detector modules 110, it isunderstood that, in some embodiments, the detector modules 110 areinstalled on or coupled to a subset of the agents 104 a-n and/or routingagents 106. For example, in some embodiments, detector modules 110 areonly included with the routing agents 106.

The detector modules 110 monitor their corresponding component (e.g.,agents 104 a-n and/or routing agents 106) to determine if a predefinedcondition is met. In some embodiments, the predefined condition includesa queue occupancy meeting a threshold. For example, a routing agent 106maintains a queue of messages and/or packets to be routed. Asnetwork-on-chip 108 traffic increases to a rate greater than the rate atwhich the routing agent 106 processes messages, the queue will increase.Thus, the detector module 110 of the routing agent 106 determines if thequeue occupancy of unrouted messages meets a threshold. As anotherexample, the predefined condition includes network-on-chip 108 trafficbeing associated with a particular class of service. For example, adetector module 110 determines if traffic generated or routed by itscorresponding component is of the particular class of service. In someembodiments, each component (e.g., agents 104 a-n and/or routing agents106) includes multiple detector modules 110. Each detector module 110for a given component monitors a different predefined condition.

In response to the predefined condition being met, the detector module110 (e.g., the detector module 110 that determined that the predefinedcondition is met) sends a signal to a mediator module 112. Each detectormodule 110 is communicatively coupled to the mediator module 112. Forexample, each detector module 110 has a direct signal path to themediator module 112 outside of the routing agents 106. Thus, the signalto the mediator module 112 need not be routed via the routing agents 106and potentially be subject to delay or slowdown in the network-on-chip108.

In response to receiving the signal, the mediator module 112 sends anindication to a plurality of agents 104 a-n to implement a trafficthrottling policy. In some embodiments, the mediator module 112 sendsthe indication by asserting a signal on direct (e.g., unrouted) signalpaths to each of the plurality of agents 104 a-n. In other embodiments,the mediator module 112 sends the indication as a message sent via therouting agents 106. In some embodiments, the indication is sent to asubset of the agents 104 a-n that generate traffic for thenetwork-on-chip 108 (e.g., those agents 104 a-n that issue transactions,excluding any agents 104 a-n that only respond to other issuedtransactions). In some embodiments, the particular traffic throttlingpolicy to be implemented is indicated in the signal or message sent tothe agents 104 a-n. In other embodiments, the traffic throttling policyis predefined or default.

By sending the indication to implement the traffic throttling policy,the mediator module 112 reduces network-on-chip 108 traffic when queueoccupancy meets a threshold, indicating that the routing agents 106 arereaching capacity. Moreover, where traffic of a particular class ofservice is detected, the implemented traffic throttling policy willimprove performance of the network-on-chip 108 and increase the overallquality of service when traffic of the particular class of service isbeing sent via the network-on-chip 108.

In some embodiments, an agent 104 a-n receiving the indication toimplement the traffic throttling policy determines to override thetraffic throttling policy. Determining to override the trafficthrottling policy includes implementing a different traffic throttlingpolicy or implementing no traffic throttling policy. For example, anagent 104 a-n generating traffic associated with a particular class ofservice will override the traffic throttling policy by implementing aless restrictive traffic throttling policy, or no traffic throttlingpolicy. As another example, an agent 104 a-n implementing a trafficthrottling policy in response to a number of outstanding transactionsmeeting a threshold continues to implement its current trafficthrottling policy, or implement a more restrictive traffic throttlingpolicy than was indicated by the mediator module 112.

In some embodiments, the detector module 110 determines that thepredefined condition is not met (e.g., no longer being met). Thedetector module 110 then indicates, to the mediator module 112, that thepredefined condition is not met. For example, where the detector module110 indicates that the predefined condition is met by asserting a signalon a communications path to the mediator module 112, indicating that thepredefined condition is not met includes deasserting the signal. Inother embodiments, indicating that the predefined condition is not metincludes sending another signal to the mediator module 112 indicatingthat the predefined condition is not met. The mediator module 112 thencauses the agents 104 a-n (e.g., the agents 104 a-n that received theindication to implement the traffic throttling policy) to end thetraffic throttling policy. For example, in some embodiments, themediator module 112 sends another signal to the agents 104 a-n to endthe traffic throttling policy. In other embodiments, the mediator module112 deasserts a signal used to indicate that the traffic throttlingpolicy should be implemented.

Although FIG. 1B describes functionality performed by a mediator module112, it is understood that, in some embodiments, the functionality ofthe mediator module 112 may instead be performed by detector modules 110of the routing agents 106 that communicate directly with the detectormodules 110 of agents 104 a-n.

For further explanation, FIG. 2 sets forth a flow chart illustrating anexemplary method for graded throttling for network-on-chip traffic. Themethod of FIG. 2 is implemented in a chip 200, such as a chip 102 a ofFIG. 1A and/or a chip 102 b of FIG. 1B. The method of FIG. 2 includescalculating 202, by an agent 104 a-n of a network-on-chip 108 (e.g.,communicatively coupled to a network-on-chip 108), a number ofoutstanding transactions issued by the agent 104 a-n. A number ofoutstanding transactions for a given agent 104 a-n is a number ofmessages sent via the network-on-chip 108 to other agents 104 a-nexpecting a response (e.g., a response to a request, an acknowledgementof receipt) that has not been received. As communication via thenetwork-on-chip 108 slows or the routing agents 106 are handlingincreased amount of traffic, the time for an agent 104 a-n to respond toa message will increase. Accordingly, the number of outstandingtransactions for a given agent 104 a-n will increase assuming the rateof transaction generation for that agent 104 a-n does not decrease.

The method of FIG. 2 also includes determining 204 that the number ofoutstanding transactions meets a threshold. The method of FIG. 2 alsoincludes implementing 206, by the agent 104 a-n, in response to thenumber of outstanding transactions meeting the threshold, a trafficthrottling policy. A traffic throttling policy is a configurable orprogramable limit at which a given agent 104 a-n generates traffic forthe network-on-chip 108. For example, assume that an agent 104 a-n ingenerating traffic for the network-on-chip 108 independent of anytraffic throttling policy (e.g., without a limit). In response to thenumber of outstanding transactions for that agent 104 a-n meeting athreshold, the agent 104 a-n will then implement a traffic throttlingpolicy to impose a limit on a rate at which the agent 104 a-n providestraffic to the network-on-chip 108.

For further explanation, FIG. 3 sets forth a flow chart illustrating anexemplary method for graded throttling for network-on-chip trafficaccording to embodiments of the present disclosure. The method of FIG. 3is similar to FIG. 2 in that the method of FIG. 3 includes calculating202 a number of outstanding transactions issued by the agent 104 a-n,determining 204 that the number of outstanding transactions meets athreshold, and implementing 206 a traffic throttling policy.

The method of FIG. 3 differs from FIG. 2 in that implementing 206, bythe agent 104 a-n, in response to the number of outstanding transactionsmeeting the threshold, a traffic throttling policy includes implementing302, based on which of a plurality of thresholds is met by the number ofoutstanding transactions, the traffic throttling policy. For example,assume the threshold is one of a plurality of thresholds and the trafficthrottling policy is one of a plurality of traffic throttling policies.Each traffic throttling policy corresponds to one of the plurality ofthresholds such that, when the number of outstanding transactions for agiven agent 104 a-n exceeds a given threshold, the corresponding trafficthrottling policy is implemented. For example, a first thresholdcorresponds to a first traffic throttling policy (e.g., a “lightthrottling policy”), a second threshold higher than the first thresholdcorresponds to a second traffic throttling policy more restrictive thanthe first traffic throttling policy (e.g., “a heavy throttling policy”),and a third threshold greater than the second threshold corresponds to athird traffic throttling policy where the agent 104 a-n ceases togenerate traffic (e.g., a “stop throttling policy”).

Using this example, where the number of outstanding transactions for anagent 104 a-n crosses the first threshold, the agent 104 a-n willimplement the light throttling policy. If the number of outstandingtransactions for the agent 104 a-n continues to increase even though thelight throttling policy is implemented, and the number crosses thesecond threshold, the agent 104 a-n will implement the heavy throttlingpolicy. Should the number continue to increase and meet the thirdthreshold, the stop throttling policy will be implemented.

For further explanation, FIG. 4 sets forth a flow chart illustrating anexemplary method for graded throttling for network-on-chip trafficaccording to embodiments of the present disclosure. The method of FIG. 4is similar to FIG. 2 in that the method of FIG. 4 includes calculating202 a number of outstanding transactions issued by the agent 104 a-n,determining 204 that the number of outstanding transactions meets athreshold, and implementing 206 a traffic throttling policy.

The method of FIG. 4 differs from FIG. 2 in that the method of FIG. 4also includes recalculating 402 (e.g., by the agent 104 a-n) the numberof outstanding transactions issued by the agent 104 a-n. For example,the agent 104 a-n continually recalculates the number of outstandingtransactions at a predefined interval, or in response to another event.The method of FIG. 4 also includes determining 404 that the number ofoutstanding transactions falls below the threshold (e.g., the previouslymet threshold). In some embodiments, determining 404 that the number ofoutstanding transactions falls below the threshold includes determiningthat the number of outstanding transactions falls below the thresholdfor a predetermined amount of time (e.g., a predefined number of clockcycles). Thus, it is determined that the number of outstandingtransactions remains below the threshold for an amount of time withoutagain meeting or exceeding the threshold. FIG. 4 also includes ending406 (e.g., in response to the number of outstanding transactions fallingbelow the threshold) the traffic throttling policy. In some embodiments,ending 406 the traffic throttling policy includes removing anyimplemented traffic throttling policy and issuing traffic to thenetwork-on-chip 108 without restriction. In other embodiments, ending406 the traffic throttling policy includes implementing another (e.g., aless restrictive) traffic throttling policy. For example, where thenumber of outstanding transactions falls below the threshold but stillexceeds another threshold, another traffic throttling policycorresponding to the other threshold is implemented.

For further explanation, FIG. 5 sets forth a flow chart illustrating anexemplary method for graded throttling for network-on-chip trafficaccording to embodiments of the present disclosure. The method of FIG. 5is similar to FIG. 4 in that the method of FIG. 5 includes calculating202 a number of outstanding transactions issued by the agent 104 a-n,determining 204 that the number of outstanding transactions meets athreshold, implementing 206 a traffic throttling policy, recalculating402 the number of outstanding transactions, determining 404 that thenumber of outstanding transactions falls below the threshold, and ending406 the traffic throttling policy.

FIG. 5 differs from FIG. 4 in that determining 404 that the number ofoutstanding transactions falls below the threshold includes determining502 that the number of outstanding transactions falls below thethreshold by a predefined amount. For example, assume that the thresholdis fifty outstanding transactions. Further assume that the number ofoutstanding transactions has exceeded the first threshold and that atraffic throttling policy is in place. Instead of removing the trafficthrottling policy when the number of outstanding transactions fallsbelow fifty, the agent 104 a-n removes the traffic throttling policywhen the number of outstanding transactions falls ten transactions belowthe threshold (e.g., forty outstanding transactions). This preventsoscillating between implementing and ending a traffic throttling policyas the number of outstanding transactions oscillates between meeting andfalling below the threshold.

For further explanation, FIG. 6 sets forth a flow chart illustrating anexemplary method for dynamic network-on-chip traffic throttling. Themethod of FIG. 6 is implemented in a chip 600, such as a chip 102 a ofFIG. 1A and/or a chip 102 b of FIG. 1B. The method of FIG. 6 includesdetermining 602, by a detector module 110 of a network-on-chip 108(e.g., corresponding to a component communicatively coupled to thenetwork-on-chip 108), that a predefined condition is met. In someembodiments, the predefined condition includes a queue occupancy meetinga threshold. For example, a routing agent 106 maintains a queue ofmessages and/or packets to be routed. As network-on-chip 108 trafficincreases to a rate greater than the rate at which the routing agent 106processes messages, the queue will increase. Thus, the detector module110 of the routing agent 106 determines if the queue occupancy ofunrouted messages meets a threshold. As another example, the predefinedcondition includes network-on-chip 108 traffic being associated with aparticular class of service. For example, a detector module 110determines if traffic generated or routed by its corresponding componentis of the particular class of service. In some embodiments, eachcomponent (e.g., agents 104 a-n and/or routing agents 106) includesmultiple detector modules 110. Each detector module 110 for a givencomponent monitors a different predefined condition.

The method of FIG. 6 also includes sending 604, by the detector module110, a signal 606 to a mediator module 112 of the network-on-chip 108.Each detector module 110 is communicatively coupled to the mediatormodule 112. For example, each detector module 110 has a direct signalpath to the mediator module 112 outside of the routing agents 106. Thus,the signal 606 to the mediator module 112 need not be routed via therouting agents 106 and potentially be subject to delay or slowdown inthe network-on-chip 108. Accordingly, sending 604 the signal 606includes asserting the signal 606 on the signaling path to the mediatormodule 112.

The method of FIG. 6 also includes sending 608, in response to thesignal 606, by the mediator module 112, an indication 610 to a pluralityof agents 104 a-n to implement a traffic throttling policy. In someembodiments, the mediator 112 sends the indication by asserting a signalon direct (e.g., unrouted) signal paths to each of the plurality ofagents 104 a-n. In other embodiments, the mediator module 112 sends theindication 610 as a message sent via the routing agents 106. In someembodiments, the indication 610 is sent to a subset of the agents 104a-n that generate traffic for the network-on-chip 108 (e.g., thoseagents 104 a-n that issue transactions, excluding any agents 104 a-nthat only respond to other issued transactions). In some embodiments,the particular traffic throttling policy to be implemented is indicatedin the signal or message sent to the agents 104 a-n. In otherembodiments, the traffic throttling policy is predefined or default.

For further explanation, FIG. 7 sets forth a flow chart illustrating anexemplary method for dynamic network-on-chip traffic throttlingaccording to embodiments of the present disclosure. The method of FIG. 7is similar to FIG. 6 in that the method of FIG. 7 includes determining602 that a predefined condition is met, sending 604 a signal 606 to amediator module 112, and sending 608, in response to the signal 606, anindication 610 to a plurality of agents 104 a-n to implement a trafficthrottling policy.

The method of FIG. 7 differs from FIG. 6 in that the method of FIG. 7also includes determining 702, by the detector module 110, that thepredefined condition is not met (e.g., no longer being met). The methodof FIG. 7 also includes indicating 704, by the detector module 110, tothe mediator module 112, that the predefined condition is not met. Forexample, where the detector module 110 indicates that the predefinedcondition is met by asserting a signal on a communications path to themediator module 112, indicating that the predefined condition is not metincludes deasserting the signal. In other embodiments, indicating thatthe predefined condition is not met includes sending another signal tothe mediator module 112 indicating that the predefined condition is notmet.

The method of FIG. 7 also includes causing 706, by the mediator module112, the plurality of agents 104 a-n (e.g., the agents 104 a-n thatreceived the indication to implement the traffic throttling policy) toend the traffic throttling policy. For example, in some embodiments, themediator module 112 sends another signal to the agents 104 a-n to endthe traffic throttling policy. In other embodiments, the mediator module112 deasserts a signal used to indicate that the traffic throttlingpolicy should be implemented.

For further explanation, FIG. 8 sets forth a flow chart illustrating anexemplary method for dynamic network-on-chip traffic throttlingaccording to embodiments of the present disclosure. The method of FIG. 8is similar to FIG. 7 in that the method of FIG. 8 includes determining602 that a predefined condition is met, sending 604 a signal 606 to amediator module 112, sending 608, in response to the signal 606, anindication 610 to a plurality of agents 104 a-n to implement a trafficthrottling policy, determining 702 that the predefined condition is notmet, indicating 704 that the predefined condition is not met, andcausing 706 the plurality of agents 104 a-n to end the trafficthrottling policy.

FIG. 8 differs from FIG. 7 in that determining 702, by the detectormodule 110, that the predefined condition is not met includesdetermining 804 that the predefined condition is not met for apredefined amount of time. The predefined amount of time is programmableor configurable. Thus, the mediator module 112 is not notified that thepredefined condition is not met until the predefined amount of time haspassed. This reduces the likelihood of the predefined conditionoscillating between occurring and not occurring, thereby reducing themediator module 112 causing oscillations between agents 104 a-nimplementing or not implementing a traffic throttling policy.

For further explanation, FIG. 9 sets forth a flow chart illustrating anexemplary method for dynamic network-on-chip traffic throttlingaccording to embodiments of the present disclosure. The method of FIG. 9is similar to FIG. 6 in that the method of FIG. 9 includes determining602 that a predefined condition is met, sending 604 a signal 606 to amediator module 112, and sending 608, in response to the signal 606, anindication 610 to a plurality of agents 104 a-n to implement a trafficthrottling policy.

The method of FIG. 9 differs from FIG. 6 in that the method of FIG. 9also includes overriding 902, by an agent 104 a-n of the plurality ofagents 104 a-n, the indication 610 to implement the traffic throttlingpolicy. In some embodiments, overriding 902 indication 610 to implementthe traffic throttling policy includes implementing a different trafficthrottling policy or implementing no traffic throttling policy. Forexample, an agent 104 a-n generating traffic associated with aparticular class of service will override the traffic throttling policyby implementing a less restrictive traffic throttling policy, or notraffic throttling policy. As another example, an agent 104 a-nimplementing a traffic throttling policy in response to a number ofoutstanding transactions meeting a threshold continues to implement itscurrent traffic throttling policy, or implement a more restrictivetraffic throttling policy than was indicated by the mediator module 112.

In view of the explanations set forth above, readers will recognize thatthe benefits of graded throttling for network-on-chip traffic include:

-   -   Improved performance of a computing system by allowing for        decentralized agents using a network-on-chip to self-regulate        their traffic throttling.    -   Improved performance of a computing system by throttling        network-on-chip traffic according to network performance.

Exemplary embodiments of the present disclosure are described largely inthe context of a fully functional computer system for graded throttlingfor network-on-chip traffic. Readers of skill in the art will recognize,however, that the present disclosure also can be embodied in a computerprogram product disposed upon computer readable storage media for usewith any suitable data processing system. Such computer readable storagemedia can be any storage medium for machine-readable information,including magnetic media, optical media, or other suitable media.Examples of such media include magnetic disks in hard drives ordiskettes, compact disks for optical drives, magnetic tape, and othersas will occur to those of skill in the art. Persons skilled in the artwill immediately recognize that any computer system having suitableprogramming means will be capable of executing the steps of the methodof the disclosure as embodied in a computer program product. Personsskilled in the art will recognize also that, although some of theexemplary embodiments described in this specification are oriented tosoftware installed and executing on computer hardware, nevertheless,alternative embodiments implemented as firmware or as hardware are wellwithin the scope of the present disclosure.

The present disclosure can be a system, a method, and/or a computerprogram product. The computer program product can include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent disclosure.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium can be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network can includecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure can be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions can execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer can be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection can be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) can execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions can be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionscan also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein includes anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions can also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams can represent a module, segment, or portionof instructions, which includes one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block can occur out of theorder noted in the figures. For example, two blocks shown in successioncan, in fact, be executed substantially concurrently, or the blocks cansometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

It will be understood from the foregoing description that modificationsand changes can be made in various embodiments of the presentdisclosure. The descriptions in this specification are for purposes ofillustration only and are not to be construed in a limiting sense. Thescope of the present disclosure is limited only by the language of thefollowing claims.

1. A method of graded throttling for network-on-chip traffic, the methodcomprising: calculating a number of outstanding transactions;determining that the number of outstanding transactions meets athreshold for a predefined duration; and in response to thedetermination, implementing a traffic throttling policy.
 2. The methodof claim 1, wherein the number of outstanding transactions comprises adifference between a number of issued transactions that have notreceived a response.
 3. The method of claim 1, wherein the threshold isincluded in a plurality of thresholds, the traffic throttling policy isincluded in a plurality of throttling policies, and implementing thetransaction policy comprises implementing, based on which of theplurality of thresholds is met by the number of outstandingtransactions, the transaction policy.
 4. The method of claim 1, furthercomprising: recalculating the number of outstanding transactions;determining that the number of outstanding transactions falls below thethreshold; and ending the traffic throttling policy.
 5. The method ofclaim 4, wherein ending the transaction policy comprises implementinganother throttling policy.
 6. The method of claim 4, wherein ending thetransaction policy comprises issuing transactions without throttling. 7.The method of claim 4, wherein determining that the number ofoutstanding transactions falls below the threshold comprises determiningthat the number of outstanding transactions falls below the threshold bya predefined amount.
 8. The method of claim 4, wherein determining thatthe number of outstanding transactions falls below the thresholdcomprises determining that the number of outstanding transactions fallsbelow the threshold for a predefined duration.
 9. A chip of gradedthrottling for network-on-chip traffic, the chip comprising anetwork-on-chip and configured to perform steps comprising: calculatinga number of outstanding transactions; determining that the number ofoutstanding transactions meets a threshold for a predefined duration;and in response to the determination, implementing a traffic throttlingpolicy.
 10. The chip of claim 9, wherein the number of outstandingtransactions comprises a difference between a number of issuedtransactions that have not received a response.
 11. The chip of claim 9,wherein the threshold is included in a plurality of thresholds, thetraffic throttling policy is included in a plurality of throttlingpolicies, and implementing the transaction policy comprisesimplementing, based on which of the plurality of thresholds is met bythe number of outstanding transactions, the transaction policy.
 12. Thechip of claim 9, wherein the steps further comprise: recalculating thenumber of outstanding transactions; determining that the number ofoutstanding transactions falls below the threshold; and ending thetraffic throttling policy.
 13. The chip of claim 12, wherein ending thetransaction policy comprises implementing another throttling policy. 14.The chip of claim 12, wherein ending the transaction policy comprisesissuing transactions without throttling.
 15. The chip of claim 12,wherein determining that the number of outstanding transactions fallsbelow the threshold comprises determining that the number of outstandingtransactions falls below the threshold by a predefined amount.
 16. Thechip of claim 12, wherein determining that the number of outstandingtransactions falls below the threshold comprises determining that thenumber of outstanding transactions falls below the threshold for apredefined duration.
 17. An apparatus graded throttling fornetwork-on-chip traffic, comprising: a chip comprising a network-on-chipand configured to perform steps comprising: calculating a number ofoutstanding transactions; determining that the number of outstandingtransactions meets a threshold for a predefined duration; and inresponse to the determination, implementing a traffic throttling policy.18. The apparatus of claim 17, wherein the number of outstandingtransactions comprises a difference between a number of issuedtransactions that have not received a response.
 19. The apparatus ofclaim 17, wherein the threshold is included in a plurality ofthresholds, the traffic throttling policy is included in a plurality ofthrottling policies, and implementing the transaction policy comprisesimplementing, based on which of the plurality of thresholds is met bythe number of outstanding transactions, the transaction policy.
 20. Theapparatus of claim 17, wherein the steps further comprise: recalculatingthe number of outstanding transactions; determining that the number ofoutstanding transactions falls below the threshold; and ending thetraffic throttling policy.